Rubber compound capable of giving a vulcanized rubber having a high modulus of elasticity

ABSTRACT

A novel rubber compound which comprises 100 parts by weight of a rubber component (I), 0.1-15 parts by weight of an amine salt of carboxylic acid (II) and 0-7 parts by weight of sulfur (III), said rubber component (I) consisting of 40-100% by weight of an elastomeric copolymer (A) and 60-0% by weight of a vulcanizable rubber (B); said elastomeric copolymer (A) being composed of a C 4  or C 5  conjugated diene, styrene, and a glycidyl group-containing monomer; the amount of said conjugated diene, the total amount of said conjugated diene and said styrene and the amount of said glycidyl group-containing monomer being 50% by weight or more, 80-99.5% weight and 0.5-20% by weight, respectively, based on the weight of said elastomeric copolymer (A); and the content of said glycidyl group-containing monomer in said rubber component (I) being 0.5% by weight or more, does not undergo scorching at the time of processing and gives, when vulcanized (crosslinked), a vulcanized rubber having a high modulus of elasticity.

This invention relates to a novel rubber compound capable of giving avulcanized rubber having a high modulus of elasticity. Moreparticularly, it relates to a rubber compound which comprises anelastomeric copolymer of a glycidyl group-containing monomer, aconjugated diene and styrene, an amine salt of carboxylic acid as acrosslinking agent, and optionally sulfur.

Recently, a vulcanized rubber having a higher modulus of elasticity thanthe general purpose vulcanized rubber (a vulcanized rubber having amodulus 1.5-3 times the 100% modulus of the conventional vulcanizedrubber) has been desired in special fields. In this case, it is, ofcourse, necessary that the rubber is comparable to the conventionalvulcanized rubber in other physical properties of vulcanizate than themodulus and is excellent in processability and workability in theunvulcanized state.

Usually, a vulcanized rubber of high modulus of elasticity has beenproduced by increasing the amount of carbon black or sulfur to becompounded with a rubber, thereby increasing the crosslinking density.According to these methods, however, the processability and workabilityof an unvulcanized rubber composition and the physical properties of avulcanized rubber are unsatisfactory, so that a desirable rubbercompound is difficult to obtain.

U.S. Pat. No. 4,094,831 teaches that the green strength of anelastomeric copolymer composed of a C₄ or C₅ conjugated diene, styreneand a glycidyl group-containing monomer can be improved by incorporatingthereinto a crosslinking agent selected from the group consisting ofmonoamines, diamines, mono-acid anhydrides, poly-acid anhydrides,monocarboxylic acids and polycarboxylic acids. However, this rubbercomposition still undergoes scorching at the time of kneading and themodulus of elasticity of the vulcanized rubber obtained from saidcomposition is not so high as to satisfy the special requirements.

The present inventors have conducted research or rubber compositionswhich can give a vulcanized rubber having a high modulus of elasticitybut do not undergo scorching at the time of processing. As a result, ithas been found that a rubber compound comprising an elastomericcopolymer consisting of a glycidyl group-containing monomer, aconjugated diene and styrene, an amine salt of carboxylic acid as acrosslinking agent, and optionally sulfur has the desired properties.

It is an object of this invention to provide a rubber compound capableof giving a vulcanized rubber having a high modulus of elasticity.

It is another object of this invention to provide a rubber compoundwhich does not undergo scorching at the time of kneading and isexcellent in processability.

It is a further object of this invention to provide a vulcanized rubberhaving a high modulus of elasticity and being excellent in otherphysical properties.

It is still another object of this invention to provide a rubbercompound excellent in processability and capable of giving a vulcanizedrubber without undergoing scorch at the time of processing, bycompounding a specified crosslinking agent with an elastomeric copolymerconsisting of a conjugated diene, styrene and a glycidylgroup-containing monomer.

Other objects and advantages of this invention will be apparent from thefollowing description.

According to this invention, there is provided a rubber compoundexcellent in processability which comprises (I) 100 parts by weight of arubber component, (II) 0.1-15 parts by weight of an amine salt ofcarboxylic acid, and (III) 0-7 parts by weight of sulfur, said rubbercomponent (I) consisting of (A) 40-100% by weight of an elastomericcopolymer composed of a C₄ or C₅ conjugated diene, styrene and aglycidyl group-containing monomer, and (B) 60-0% by weight of a rubber;the total amount of said conjugated diene and said styrene, the contentof said glycidyl group-containing monomer and the content of saidconjugated diene in said elastomeric copolymer (A) being 80-99.5% byweight, 0.5-20% by weight and at least 50% by weight, respectively; andthe content of said glycidyl group-containing monomer in said rubbercomponent (I) being 0.5% by weight or more.

The copolymer (A) used in this invention is composed of a C₄ or C₅conjugated diene, styrene and a glycidyl group-containing monomer,wherein the content of said conjugated diene is 50% by weight or more,the total quantity of said conjugated diene and said styrene is 80-99.5%by weight, and the content of said glycidyl group-containing monomer is0.5-20% by weight. Said C₄ or C₅ conjugated diene includes butadiene,isoprene, 1,3-pentadiene and mixtures thereof, among which butadiene andisoprene are preferable, and butadiene is particularly preferable. Assaid glycidyl group-containing monomer, there may be used monomershaving a glycidyl group and being copolymerizable with styrene andconjugated diene. Specific examples of said glycidyl group-containingmonomer include glycidyl methacrylate, glycidyl acrylate, glycidyl allylether and the like, among which glycidyl methacrylate is preferable.

The content of styrene in copolymer (A) is preferably 5% by weight ormore and 45% by weight or less from the viewpoint of processability. Thecontent of conjugated diene in copolymer (A) has to be at least 50% byweight, because if its content is less than 50% by weight the copolymer(A) obtained does not have rubber properties suitable for use in thisinvention. That is, if its content is less than 50%, the vulcanizedrubber obtained from the rubber compound of this invention cannot retaina high modulus of elasticity at high temperatures and generates muchheat when subjected to repeated deformations. If the content of saidglycidyl group-containing monomer in rubber component (I) is less than0.5% by weight, the vulcanized rubber obtained cannot have a highmodulus of elasticity. If the content of said glycidyl group-containingmonomer in copolymer (A) is more than 20% by weight, the elongation atbreak of the vulcanized rubber drops.

Said elastomeric copolymer is usually produced by emulsionpolymerization, though it may also be produced by other polymerizationprocesses.

As said crosslinking agent, there are used amine salts of carboxylicacids which can react with the epoxy group of said glycidylgroup-containing monomer at a temperature equal to or higher than thevulcanization temperature. As said amine, there may be used primary,secondary and tertiary monoamines and polyamines, among which aliphaticand alicyclic mono- and di-amines having 1-20 carbon atoms arepreferred. Polyamines having two or more amino groups selected fromprimary, secondary and tertiary amino groups can also be used. As saidmonoamine, there may be used primary amines such as ethylamine,butylamine and ethanolamine, secondary amines such as diethylamine,dibutylamine and piperidine and tertiary amines such as tributylamine.As said polyamine, there may be used primary diamines such ashexamethylenediamine, p-phenylenediamine and the like, secondarydiamines such as N,N'-dimethylethylenediamine,N,N'-dimethyl-p-phenylene-diamine, piperazine and the like, and teriarydiamines such as triethylenediamine and the like. Further,diethylenetriamine, triethylenetetramine, hexamethylenetetramine,polyethyleneimine and the like may also be used. Among these amines,alicyclic amine compounds and aliphatic amine compounds are preferred.Specifically, diamines such as piperazine, hexamethylenediamine and thelike and monoamines such as piperidine and the like are preferable,among which piperazine is particularly preferable.

As the carboxylic acid forming a salt with said amine, there may be usedaliphatic, alicyclic and aromatic monocarboxylic and dicarboxylic acidshaving 2-20 carbon atoms such as acetic acid, butyric acid, octanoicacid, stearic acid, cyclohexanoic acid, cyclohexanedicarboxylic acid,benzoic acid, toluic acid, oxalic acid, malonic acid, succinic acid,adipic acid, sebacic acid, and phthalic acid; hydroxyl group-containingaliphatic and aromatic carboxylic acids having 2-20 carbon atoms such asglycolic acid, malic acid, lactic acid, citric acid, and p-oxybenzoicacid; and thiol group-containing aliphatic carboxylic acids having 2-10carbon atom such as thioglycolic acid. Among these acids, the hydroxylgroup-containing carboxylic acids are preferable, and glycolic acid,malic acid, lactic acid and p-oxybenzoic acid are particularlypreferable.

The crosslinking agent is added in an amount of 0.1-15 parts by weightand preferably 1-10 parts by weight per 100 parts by weight of rubbercomponent (I). If its amount is less than 0.1 part by weight, avulcanized rubber having a high modulus of elasticity cannot beobtained. If it is more than 15 parts by weight, the crosslinking agentcauses blooming, which is undesirable. By using the specifiedcrosslinking agent, namely a salt formed between the above-mentionedamine and the above-mentioned carboxylic acid, particularly the hydroxylgroup-containing or thiol group-containing carboxylic acid, in aspecified amount, there can be obtained a rubber compound capable ofgiving a vulcanized rubber having a high modulus of elasticity andmarkedly improved in anti-scorch property.

Although the glycidyl group-containing elastomeric copolymer (A) may beused alone in this invention, it may also be used in combination with60% by weight or less, preferably 50% by weight or less, of anothervulcanizable rubber (B). If the amount of vulcanizable rubber (B)exceeds 60% by weight, the characteristic properties of the glycidylgroup-containing elastomeric copolymer cannot fully be exhibited, sothat a rubber of high modulus is difficult to obtain. Accordingly, it isnecessary that the glycidyl group-containing monomer exists in therubber component (I) in an amount of 0.5% by weight or more.

On the other hand, it is also possible to blend the rubber compound ofthis invention with a general purpose rubber in order to enhance themodulus of elasticity of vulcanizate without injuring the characteristicproperties of rubber. In this case, the compound of this invention isblended in an amount of 10% or more and less than 40%; the content ofglycidyl group-containing monomer in the total rubber component being0.5% by weight or more; and, preferably, the proportions of the aminesalt of carboxylic acid and the sulfur to the total rubber component are0.1 part by weight or more and 0.5 part by weight or more, respectively,per 100 parts by weight of the total rubber component. As said generalpurpose rubber, the same rubber as the rubber of component (B) may beused. As the vulcanizable rubber (B), there may be exemplified naturalrubber, polyisoprene, polybutadiene, styrene-butadiene rubber,ethylene-propylene rubber, butyl rubber, chloroprene rubber, nitrilerubber and the like, among which natural rubber, polyisoprene,polybutadiene and styrene-butadiene rubber are preferred.

In this invention, it is, of course, possible to make crosslinkage withonly an amine salt of carboxylic acid. It is particularly preferable,however, to use sulfur in combination therewith from the viewpoint ofobtaining a vulcanized rubber having a high modulus of elasticity. Inthis case, the sulfur is used in an amount of 7 parts or less andpreferably 5 parts or less per 100 parts by weight of rubber component(I). When the glycidyl group-containing elastomeric copolymer (A) isblended with vulcanizable rubber (B), the use of sulfur is necessary. Inthis case, the amount of the sulfur is 0.5-7 parts by weight per 100parts by weight of rubber component (I).

Conveniently, the addition of the crosslinking agent and sulfur iseffected with kneading by means of an open mill or a mixer. The rubbercompound of this invention is vulcanized by heating it at a temperatureof, for example, 60°-200° C. and preferably 100°-170° C. for 10 minutesto 5 hours. As the mode of heating, either open system or press systemmay be selected depending on the shape of the object to be heated.

With the rubber compound of this invention may be compounded thosereinforcing materials, fillers, processing aids, antioxidants, and otheradditives which are conventionally compounded with rubbers. However, itis undesirable to add an additive reactive with the glycidyl group inaddition to the functional crosslinking agent and said additivesthroughout the whole production process including the polymerizationstep. Said additives may be blended by means of a roll or a Banburymixer, or they may also be added in the course of producing the polymer.

The rubber compound of this invention is excellent in processabilityand, at the same time, quite excellent in anti-scorch effect, and it cangive a vulcanized rubber having a high modulus of elasticity. Thevulcanized rubber retains the high modulus of elasticity though only asmall drop may occur at high temperatures. The rubber composition ofthis invention is comparable in processability to commercial blends ofemulsion-polymerized SBR, and it is particularly easy to mix with carbonblack. The vulcanized rubber usually has a 50% modulus of 25 kg/cm² ormore and a 100% modulus of 50 kg/cm² or more. Accordingly, the rubbercompound of this invention is useful in the fields requiring a highmodulus of elasticity such as tire, rubber vibration insulator, bumper,belt, flexible joint, guide roller, ship's side protector, hose, packingmaterial, sealing material and the like.

With reference to Examples and the accompanying drawings, this inventionwill be illustrated below.

In the accompanying drawings, FIG. 1 shows a graph of vulcanizationcurve which is presented for the purpose of explaining scorch time(t'_(c) (10)), and;

FIG. 2 and FIG. 3 show graphs of vulcanization curve in the Examples ofthis invention and the Comparative Examples, which appear hereinafter.

PRODUCTION OF ELASTOMERIC COPOLYMER

The glycidyl methacrylate (abbreviated hereinafter toGMA)-butadiene-styrene copolymer used in the Examples appearinghereinbelow was synthesized in the following manner. In the descriptionsgiven below, parts and % are all by weight unless otherwise specified.

Polymers A and B in Table 1 were produced from 72 parts of butadiene, 26parts of styrene and 2 parts of GMA, polymers C, E and F in Table 1 from72 parts of butadiene, 24 parts of styrene and 4 parts of GMA, andpolymer D in Table 1 from 72 parts of butadiene, 22 parts of styrene and6 parts of GMA, by the conventional emulsion polymerization process. Thepolymerization temperature was 5° C. and the conversion was about 60% inall the cases. The results of polymerization are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Kind of [n].sup.1             Content of GMA.sup.2                            polymer (dl/g)   ML.sub.1+4.sup.100° C.                                                              (%)                                             ______________________________________                                        A       1.83     44.5         3.3                                             B       2.14     69           3.3                                             C       2.15     57           6.7                                             D       2.18     79           9.6                                             E       2.25     68           6.7                                             F       2.05     47.5         6.7                                             ______________________________________                                         .sup.1 Measured in toluene at 30° C.                                   .sup.2 Measured by infrared absorption spectroscopy.                     

The polymers synthesized by the procedure mentioned above were blendedand kneaded according to the recipe shown in Table 2. Then, on the onehand, polymers were vulcanized and the vulcanizates were subjected totensile test in accordance with JIS K 6301. On the other hand, theirvulcanization curves were measured by means of a curemeter (JSRCURELASTOMETER®, manufactured by Japan Synthetic Rubber Co., Ltd.)(measurement temperature: 145° C.), whereby the anti-scorch effect wasevaluated. That is to say, when the torque at the start of measurementis higher than that of the system free from the crosslinking agent andcontaining sulfur only, it is judged that crosslinking reaction (namelyscorching) has been caused before the start of vulcanization. On theother hand, when the torque at the start of measurment is the same asthat of the system free from the crosslinking agent and containingsulfur only, the time taken until the crosslinking reaction begins(t_(o)) is measured, and also the time taken until the torque reachesthe value of [M_(L) +0.1(M_(H) -M_(L))] where M_(L) is the minimum oftorque in the vulcanization curve and M_(H) is the maximum of torque inthe same curve (t'_(c) (10)) is determined from the vulcanization curve.The larger the t_(o) and t'_(c) (10) values, the more excellent theanti-scorch effect. On the other hand, when the t_(o) value is less than0.5 min and the t'_(c) (10) value is less than 1.0 min, the start ofvulcanization is too early and therefore, the vulcanizing processabilityis inferior. Thus, such a case is not desirable. Accordingly, in such acase, it is judged that the rubber compound has no anti-scorch effect.

                  TABLE 2                                                         ______________________________________                                        Compounding Recipe (parts by weight)                                                             Recipe      Recipe                                         Component          [I]         [II]                                           ______________________________________                                        Polymer            100         100                                            Carbon black       50          50                                             Aromatic oil       10          10                                             Zinc oxide          5           5                                             Stearic acid        3           3                                             Accelerator (N-oxydiethylene-                                                 2-benzothiazole sulfenamide)                                                                     1.5         --                                             Sulfur             2.5         --                                             Crosslinking agent Varying     Varying                                        ______________________________________                                    

The vulcanization conditions were 60 min at 145° C., provided that inExamples 16-19 and Comparative Example 6, press vulcanization wascarried out for 45 min at 145° C.

EXAMPLES 1 AND 2 AND COMPARATIVE EXAMPLES 1 AND 2

Piperazine malate was used as the crosslinking agent in Example 1, andpiperazine citrate was used as the crosslinking agent in Example 2. Theresults obtained are shown in Table 3. For comparison, the resultsobtained where no crosslinking agent was used (Comparative Example 1)and piperazine was used as the crosslinking agent (Comparative Example2) are also shown in Table 3. All the crosslinking agents were used inthe same molar amount.

                                      TABLE 3                                     __________________________________________________________________________           Kind Crosslinking agent                                                Example                                                                              of         Amount   M.sub.100.sup.2                                                                    T.sub.B.sup.3                                                                      E.sub.B.sup.4                                                                    t.sub.o                                                                           t.sub.c '(10)                     No.    polymer                                                                            Kind  (PHR).sup.1                                                                        Recipe                                                                            (kg/cm.sup.2)                                                                      (kg/cm.sup.2)                                                                      (%)                                                                              (min)                                                                             (min)                             __________________________________________________________________________    1      A    Pierazine                                                                           2.56 [I] 56   212  268                                                                              3.3 6.8                                           malate                                                            2      A    Piperazine                                                                          2.49 [I] 54   163  195                                                                              3.3 6.8                                           citrate                                                           Comparative                                                                   Example 1                                                                            A    --         [I] 32   216  373                                                                              6.3 16.0                              Comparative                                                                   Example 2                                                                            A    Piperazine                                                                          1    [I] 52   228  343                                                                              --  --                                __________________________________________________________________________     Note:                                                                         .sup.1 PHR means parts per 100 parts by weight of rubber.                     .sup.2 M.sub.100 means 100% modulus.                                          .sup.3 T.sub.B means tensile strength at break.                               .sup.4 E.sub.B means elongation at break.                                

The vulcanization curves obtained in Examples 1 and 2 and ComparativeExample 2 are shown in FIG. 2.

It can be seen that the intended rubbers having a high modulus areobtained in Examples 1 and 2 and the rubbers thus obtained are excellentin anti-scorch effect. On the other hand, Comparative Example 1 showsvulcanization with sulfur only, and the modulus of the vulcanizateobtained is low. In Comparative Example 2, it is seen from FIG. 2 thatscorching takes place before vulcanization, because the torque at thevulcanization time of zero is higher than in the other cases as observedon the vulcanization curve.

EXAMPLE 3

Piperazine p-oxybenzoate was used alone as the crosslinking agent. Theresults obtained are shown in Table 4.

The vulcanization curve obtained is shown in FIG. 2.

                                      TABLE 4                                     __________________________________________________________________________    Kind      Crosslinking agent                                                  Example                                                                            of         Amount   M.sub.100                                                                          T.sub.B                                                                            E.sub.B                                                                          t.sub.o                                                                           t.sub.c '(10)                       No.  polymer                                                                            Kind  (PHR)                                                                              Recipe                                                                            (kg/cm.sup.2)                                                                      (kg/cm.sup.2)                                                                      (%)                                                                              (min)                                                                             (min)                               __________________________________________________________________________              Piperazine                                                          3    C    p-oxyben-                                                                           8.42 [II]                                                                              77   178  224                                                                              1.3 3.1                                           zoate                                                               __________________________________________________________________________

EXAMPLES 4 AND 5 AND COMPARATIVE EXAMPLE 3

Piperazine glycolate was used as the crosslinking agent and the amountthereof was varied. The amount of the crosslinking agent used in Example5 was equimolar to that in Comparative Example 3, while that in Example4 was one half thereof. The results obtained are shown in Table 5.

                                      TABLE 5                                     __________________________________________________________________________           Kind Crosslinking agent                                                Example                                                                              of         Amount   M.sub.100                                                                          T.sub.B                                                                            E.sub.B                                                                          t.sub.o                                                                           t.sub.c '(10)                     No.    polymer                                                                            Kind  (PHR)                                                                              Recipe                                                                            (kg/cm.sup.2)                                                                      (kg/cm.sup.2)                                                                      (%)                                                                              (min)                                                                             (min)                             __________________________________________________________________________    4      B    Piperazine                                                                          2.27 [I] 56   169  221                                                                              1.8 5.3                                           glycolate                                                         5      B    Piperazine                                                                          5.53 [I] 83   171  173                                                                              2.0 3.5                                           glycolate                                                         Comparative                                                                          B    Piperazine                                                                          2    [I] 76   174  160                                                                              --  --                                Example 3                                                                     __________________________________________________________________________

The vulcanization curves obtained in Examples 4 and 5 and ComparativeExample 3 are shown in FIG. 3. In Comparative Example 3, the torque atthe start was great and scorching was observed.

EXAMPLES 6 AND 7

Piperazine salts of monocarboxylic acids were used as the crosslinkingagent in Recipe [I] in which polymer E was used. The results obtainedare shown in Table 6. It is seen that Examples 6 and 7 gave the intendedhigh modulus rubber excellent in anti-scorch effect.

                                      TABLE 6                                     __________________________________________________________________________                                         Measurement by                           Crosslinking agent                                                                             Properties of vulcanizate                                                                         curemeter                                Example     Amount                                                                             M.sub.50                                                                           M.sub.100                                                                          T.sub.B                                                                            E.sub.B                                                                            t.sub.o                                                                            t.sub.c '(10)                       No.   Kind  (PHR)                                                                              (kg/cm.sup.2)                                                                      (kg/cm.sup.2)                                                                      (kg/cm.sup.2)                                                                      (%)  (min)                                                                              (min)                               __________________________________________________________________________    6     Piperazine                                                                          4.35 39   84   228  219  1.0  6.0                                       octanoate                                                               7     Piperazine                                                                          3.84 31   66   194  246  1.0  8.4                                       benzoate                                                                __________________________________________________________________________

EXAMPLES 8-11 AND EXAMPLES 4-6

Piperazine salts of hydroxyl-containing monocarboxylic acid were used asthe crosslinking agent in Recipe [I] in which polymer E was used, andthe results obtained are shown in Table 7. It is seen that the intendedhigh modulus rubber was obtained and the rubber obtained was excellentin anti-scorch effect. On the other hand, in Comparative Example 4, therubber was vulcanized with sulfur alone, and the vulcanizate did nothave a high modulus. In Comparative Example 5, the compound Mooneyviscosity was too high, and the processability was deteriorated.Measurement of vulcanization curve reveals that the torque at the startof measurement is higher than that of the system vulcanized with sulfuralone (Comparative Example 4). Comparative Example 6 demonstrates thatthe intended high modulus rubber cannot be obtained by compounding ahydroxyl-containing monocarboxylic acid itself only.

                                      TABLE 7                                     __________________________________________________________________________                             Compound                                                                             Green                  Measurement                   Crosslinking agent                                                                              mooney strength                                                                           Properties of vulcanizate                                                                       by curemeter           Example             Amount                                                                             viscosity                                                                            T.sub.max                                                                          M.sub.50                                                                           M.sub.100                                                                          T.sub.B                                                                            E.sub.B                                                                          t.sub.o                                                                           t.sub. c                                                                      '(10)              No.    Kind         (PHR)                                                                              ML.sub.1+4.sup.100° C.                                                        (kg/cm.sup.2)                                                                      (kg/cm.sup.2)                                                                      (kg/cm.sup.2)                                                                      (kg/cm.sup.2)                                                                      (%)                                                                              (min)                                                                             (min)              __________________________________________________________________________    Comparative                                                                   Example 4                                                                            -- (S only)  --   59.5   4.0  19   37   203  351                                                                              7.3 21.1               Comparative                                                                   Example 5                                                                            Piperazine   1    142.0  26.1 57   122  204  169                                                                              Scorch                 Comparative                                                                   Example 6                                                                            Glycolic acid                                                                              1.77 63.0   4.2  20   40   173  231                                                                              11.4                                                                              29.2               Example 8                                                                            Piperazine glycolate                                                                       2.77 68.0   5.1  35   77   194  218                                                                              1.5 6.7                Example 9                                                                            Piperazine p-oxybenzoate                                                                   4.21 65.0   5.5  36   83   168  187                                                                              1.9 6.9                Example 10                                                                           Piperazine oxalate                                                                         2.05 62.0   4.5  25   51   152  231                                                                              2.5 15.8               Example 11                                                                           Piperazine malonate                                                                        2.21 64.0   4.8  33   72   197  226                                                                              0.8 6.3                __________________________________________________________________________

EXAMPLES 12-15 AND COMPARATIVE EXAMPLES 7 AND 8

The hexamethylenediamine salts of carboxylic acids were used as thecrosslinking agent in Recipe [I] in which polymer F was used. Theresults obtained are shown in Table 8. It is seen that both theglycolate and the nylon salts give the intended high modulus rubbersexcellent in anti-scorch effect. On the other hand, the rubber obtainedin Comparative Example 7 has a high compound Mooney viscosity and a lowprocessability. Measurement of vulcanization curve reveals that thetorque at the start of measurement is higher than that in the systemvulcanized with sulfur alone. Comparative Example 8 demonstrates thatthe intended high modulus rubber cannot be obtained by compounding thecarboxylic acid alone.

                                      TABLE 8                                     __________________________________________________________________________                             Compound                                                                             Green                  Measurement                   Crosslinking agent                                                                              Mooney strength                                                                           Properties of vulcanizate                                                                       by curemeter           Example             Amount                                                                              viscosity                                                                           T.sub.max                                                                          M.sub.50                                                                           M.sub.100                                                                          T.sub.B                                                                            E.sub.B                                                                          t.sub.o                                                                           t.sub. c '                                                                    (10)               No.    Kind         (PHR)                                                                              ML.sub.1+4.sup.100°  C.                                                       (kg/cm.sup.2)                                                                      (kg/cm.sup.2)                                                                      (kg/cm.sup.2)                                                                      (kg/cm.sup.2)                                                                      (%)                                                                              (min)                                                                             (min)              __________________________________________________________________________    Comparative                                                                   Example 7                                                                            Hexamethylenediamine                                                                       1.35 154.0  36.2 46   97   217  238                                                                              Scorch                 Comparative                                                                   Example 8                                                                            Adipic acid  1.70 67.5   4.5  19   35   127  281                                                                              5.0 21.6               Example 12                                                                           6,6-nylon salt.sup.1                                                                       3.05 65.0   4.8  25   52   112  178                                                                              1.9 5.5                Example 13                                                                           6,10-nylon salt.sup.2                                                                      3.70 --     5.1  31   61   180  254                                                                              2.0 4.4                Example 14                                                                           6,4-nylon salt.sup.3                                                                       2.72 --     5.0  30   63   178  234                                                                              2.8 5.5                Example 15                                                                           Hexamethylenediamine                                                                       4.62 --     --   30   64   204  259                                                                              1.8 4.0                       glycolate                                                              __________________________________________________________________________     .sup.1 Hexamethylenediamine adipate                                           .sup.2 Hexamethylenediamine sebacate                                          .sup.3 Hexamethylenediamine succinate                                    

EXAMPLE 16

Piperidine glycolate (monoamine salt of carboxylic acid) was used as thecrosslinking agent. The results obtained are shown in Table 9.

                                      TABLE 9                                     __________________________________________________________________________    Kind      Crosslinking agent                                                  Example                                                                            of          Amount   M.sub.100                                                                          T.sub.B                                                                            E.sub.B                                                                          t.sub.o                                                                           t.sub.c '(10)                      No.  polymer                                                                            Kind   (PHR)                                                                              Recipe                                                                            (kg/cm.sup.2)                                                                      (kg/cm.sup.2)                                                                      (%)                                                                              (min)                                                                             (min)                              __________________________________________________________________________    16   C    Piperidine                                                                           4.0  [I] 51    194 286                                                                              1.5 4.1                                          glycolate                                                           17   E    2-Butylamine                                                                         4.53 [I] 50   203  282                                                                              1.5 6.3                                          benzoate                                                            __________________________________________________________________________

It is seen from Table 9 that the monoamine salt of a carboxylic acidsimilarly produces the intended high modulus rubber excellent inanti-scorch effect.

EXAMPLES 18-21 AND COMPARATIVE EXAMPLE 9

The GMA-containing SBR of this invention was blended with other rubbers.The recipes used are shown in Table 10 and the results obtained areshown in Table 11.

                                      TABLE 10                                    __________________________________________________________________________    Recipes                                                                                     Example                                                                            Example                                                                            Example                                                                            Example                                                                            Comparative                                               18   19   20   21   Example 9                                   __________________________________________________________________________    NR            0    25   50   75   100                                         Polymer D     100  75   50   25   0                                           Carbon black  50   50   50   50   50                                          Aromatic oil  10   10   10   10   10                                          Zinc oxide    5    5    5    5    5                                           Stearic acid  3    3    3    3    3                                           Dibenzothiazolyl disulfide                                                                  1.5  1.3  1.1  0.9  0.7                                         Tetramethylthiuram disulfide                                                                0.2  0.15 0.1  0.05 0                                           Sulfur        2.5  2.5  2.5  2.5  2.5                                         Piperazine glycolate                                                                        2.77 2.07 1.39 0.69 0                                           __________________________________________________________________________

                  TABLE 11                                                        ______________________________________                                        Example  M.sub.100 T.sub.B  E.sub.B                                                                             t.sub.o                                                                              t.sub.c '(10)                        No.      (kg/cm.sup.2)                                                                           (kg/cm.sup.2)                                                                          (%)   (min)  (min)                                ______________________________________                                        18       96        174      159   1.0    3.0                                  19       79        151      167   1.3    2.8                                  20       57        148      211   1.5    2.9                                  21       38        156      299   1.8    2.8                                  Comparative                                                                   Example 9                                                                              19        145      411   2.0    2.8                                  ______________________________________                                    

What is claimed is:
 1. A rubber compound, which comprises:(1) 100 partsby weight of a rubber component, (2) 0.1-15 parts by weight of an aminesalt of a carboxylic acid, and (3) 0-7 parts by weight of sulfur, saidrubber component (1) comprising an elastomeric copolymer being composedof a C₄ or C₅ conjugated diene, styrene and a glycidyl group-containingmonomer; the content of said conjugated diene, the total amount of saidconjugated diene and said styrene and the content of said glycidylgroup-containing monomer in said elastomeric copolymer being 50% byweight or more, 80-99.5% by weight and 0.5-20% by weight, respectively.2. The rubber compound according to claim 1, wherein said amine salt ofa carboxylic acid is a salt formed between a carboxylic acid selectedfrom the group consisting of C₂ -C₂₀ aliphatic monocarboxylic ordicarboxylic acids; alicyclic monocarboxylic or dicarboxylic acidshaving 20 carbon atoms or less; aromatic monocarboxylic or dicarboxylicacids having 20 carbon atoms or less and C₂ -C₂₀ carboxylic acids havinghydroxyl groups or thiol groups, and an amine selected from the groupconsisting of C₁ -C₂₀ aliphatic or alicyclic monoamines and polyamines.3. The rubber compound according to claim 1, wherein said amine salt ofcarboxylic acid is an amine salt of a carboxylic acid having hydroxylgroup or thiol group.
 4. The rubber compound according to claim 1 or 2,wherein said amine is a monoamine or a diamine.
 5. The rubber compoundaccording to claim 1 or 2, wherein said amine salt of carboxylic acid isa piperazine salt.
 6. The rubber compound according to claim 1 or 2,wherein said amine salt of carboxylic acid is a piperidine salt.
 7. Therubber compound according to claim 1 or 2, wherein said carboxylic acidis selected from the group consisting of acetic acid, butyric acid,octanoic acid, stearic acid, benzoic acid, toluic acid, oxalic acid,malonic acid, succinic acid, adipic acid, sebacic acid, phthalic acid,glycolic acid, malic acid, lactic acid, citric acid, p-oxybenzoic acid,and thioglycolic acid.
 8. The rubber compound according to claim 1 or 2,wherein said carboxylic acid is selected from the group consisting ofglycolic acid, malic acid, lactic acid and p-oxybenzoic acid.
 9. Therubber compound according to claim 1 or 2, wherein said amine isselected from the group consisting of ethylamine, butylamine,ethanolamine, diethylamine, dibutylamine, piperidine, ethyleneimine,tributylamine, hexamethylenediamine, p-phenylenediamine,N,N'-dimethylethylenediamine, N,N'-dimethyl-p-phenylenediamine,piperazine, triethylenediamine, diethylenetriamine,triethylenetetramine, hexamethylenetetramine and polyethyleneimine. 10.The rubber compound according to claim 1 or 2, wherein said amine isselected from the group consisting of piperazine, hexamethylenediamineand piperidine.
 11. The rubber compound according to claim 5, whereinsaid carboxylic acid is glycolic acid, malic acid, lactic acid orp-oxybenzoic acid.
 12. The rubber compound according to claim 6, whereinsaid carboxylic acid is glycolic acid, malic acid, lactic acid, orp-oxybenzoic acid.
 13. The rubber compound according to claim 1, whereinthe content of sulfur is 0.5-7 parts by weight based on 100 parts byweight of the rubber component (I).
 14. The rubber compound according toclaim 1, 2 or 3, wherein the amount of said amine salt of saidcarboxylic acid added is 1-10 parts by weight per 100 parts by weight ofrubber component (I).
 15. The rubber compound according to claim 1,wherein said amine salt of a carboxylic acid is the hexamethylenediaminesalt of adipic acid, sebacic acid or succinic acid.